1. Field of the Invention
The present invention relates to a method for manufacturing an electronic apparatus.
2. Description of the Related Art
Generally, in an electronic apparatus, components are mounted on both first and second surfaces of a substrate, thus increasing the density of mounted components. In this case, a cavity is provided on the first surface of the substrate, and a component is mounted on the first surface of the substrate within the cavity. Then, the apparatus is reversed, and another component is mounted on the second surface of the substrate. Note that, unless the cavity is provided on the surface of the substrate, it is impossible to reverse the apparatus.
In a first prior art method (see JP-A-3-211763), the substrate is made of ceramic. Therefore, since the substrate is rigid, semiconductor chips are mounted on both the first and second surfaces of the substrate and stable wire bonding operations are performed thereupon. Also, the semiconductor chips are sealed by convex thermosetting resin envelopers. This will be explained later in detail.
In the first prior art method, however, in order to compensate for the fluctuation of height of the molded resin enveloper, the depth of the cavity is made large. As a result, a step between the molded resin enveloper and the first surface of the substrate becomes large. This makes it difficult to determine whether or not the appearance of the molded resin enveloper is bad, i.e., whether or not the molded resin enveloper is protruded from the cavity. Note that if the molded resin enveloper is protruded from the cavity, it is impossible to reverse the apparatus for preparing the wire bonding operation performed upon the second surface of the substrate. Also, the above-mentioned large step increases the size of the apparatus. Further, the ceramic substrate is heavy and expensive. Still further, it is difficult to mount this apparatus on an organic mounting board which is broadly used, since a difference in thermal expansibility between the ceramic substrate and the organic mounting board creates stress therebetween, so that cracks and disconnections may be generated in the ceramic substrate and the organic mounting board as time passes.
In a second prior art method (see JP-A-5-259372) the substrate is made of organic material. This also will be explained later in detail.
In the second prior art method, however, since the organic substrate is flexible, a stable wire bonding operation cannot be performed upon the second surface of the organic substrate. This reduces the density of mounted chips.
Also, in the second prior art method, in order to compensate for the fluctuation of height of the molded resin enveloper, the depth of the cavity is made large. As a result, a step between the molded resin enveloper and the first surface of the substrate becomes large. This makes it difficult to determine whether or not the appearance of the molded resin enveloper is bad, i.e., whether or not the molded resin enveloper is protruded from the cavity.
Further, in the second prior art method, if the apparatus is large, a difference in thermal expansibility between the substrate and the molded resin enveloper makes the apparatus warp, so that it is impossible to amount the apparatus on a mounting board.